I. Field of the Invention
The present invention relates to power buckets or grabs for loading and unloading cargo.
II. Description of the Prior Art
The previously known clam shell buckets of the type used with power shovels typically comprise a pair of bucket halves which are pivotally secured together adjacent to their upper end. The upper end of the bucket is also known as the bucket "head" and this head is connected by a cable to a power mechanism which raises and lowers the bucket. Additionally, a closure cable is secured to the bucket halves for moving the bucket halves between their open and closed positions.
A primary disadvantage of these previously known buckets is that the buckets are made of a cast construction. The cast construction is not only expensive to manufacture but also significantly increases the overall weight of the bucket. This, in turn, reduces the overall cargo capacity of the bucket since the capacity of the power shovel is determined not only by the weight of the cargo within the bucket, but also the weight of the bucket itself. For example, if the power winch for raising the bucket is capable of lifting fifteen tons and the bucket itself weighs five tons, then only ten tons of cargo can be lifted by the power shovel.
One reason for the excessive weight of these previously known grabs or buckets is that the head is cast as a one piece construction with at least one of the bucket halves so that the extra metal between the head and the bucket half significantly increases the overall weight of the bucket. Additionally, a cast construction is typically relatively thick which also increases the overall weight of the bucket.
In order to overcome some of the above described disadvantages of the previously known clam shell buckets, there are a number of previously known buckets which have a head disposed above a pair of bucket halves. The bucket halves are in turn pivotally mounted together and suspended from the head by elongated cables. Examples of such buckets are disclosed in my prior U.S. Pat. Nos. 4,998,762 and 5,029,923.
In these previously known power buckets of the type in which the bucket halves are suspended from the head by cables, the bucket halves are typically pivotally secured together by an elongated tubular shaft extending through registering journals on the bucket halves. This construction, however, has not proven wholly satisfactory in operation.
One disadvantage of this previously known construction is that the shaft as well as the registering journals formed in the bucket halves are relatively expensive not only in material costs, but also in labor in order to construct the pivot shaft with its associated journals. Furthermore, any misalignment of the pivot shaft with its journals will rapidly result in excessive wear and necessitate expensive repairs for the bucket.
A still further disadvantage of this previously known type of bucket is that disassembly of the bucket halves for repair or other reasons is not only difficult but, in many cases, impossible without destruction of the pivot shaft.
A still further disadvantage of these previously known power buckets is that the closure cable was unattached with respect to the head. As such, the closure cable was prone to wild swings during operation of the bucket. Such wild swings of the closure cable not only creates a safety hazard, but can also damage the cable as well as the head.